Incandescent lamp.



Patented .Dec. l2, I899.

R. A. FESSENDEN.

INGANDESCENT LAMP.

Applicution filed Aug. 25, 1899 2 Sheets-Sheet (N 0 Model.)

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Tn: NORRIS mans co. PHOTOLVTNOV, WASHINGYON. n. c.

No. 638,840. Patented Dec. l2, I899.

R. A. FESSENDEN.

INCANDESCENT LAMP.

(Application filed Aug-L 25, 1899.)

2 Sheets-Sheet 2.

(No Model.)

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wire STATES ATENT FFICE.

REGINALD A. FESSENDEN, OF ALLEGHENY, PENNSYLVANIA, ASSIGNOR OF ONE-HALF TO GRANT MOOARGO, OF PITTSBURG, PENNSYLVANIA.

INCANDESCENT LAMP.

SPECIFICATION forming part of Letters Patent No. 638,840, dated December 12, 1899.

Application filed August 25, 1899.

T0 aZZ whom it may concern:

Be it known that LREGINA'LD A.FESSENDEN, a citizen of the United States, residing at Allegheny, in the county of Allegheny and State of Pennsylvania, have invented or discovered certain new and useful Improvements in Incandescent Lamps, of which improvements the following is a specification.

The invention described herein relates to certain improvements in incandescent lamps, but especially in that class or kind of incandescent lamps described and shown in applications Serial No. 726,395, filed August 7,1899, and Serial No. 728,421, filed August 25, 1899. Generally stated, these lamps employ a pencil formed of a material, as thoria, magnesia, or kaolin, which is a non-conductor at normal temperature, but becomes a good conductor when heated,the conductivity increasing with increase in temperature. It follows from this characteristic of the material that i any increase in temperature will reduce the resistance, so that more current will flow through the pencil. By this increased flow of current the temperature of the pencil will be raised, thereby permitting of a still greater flow of current with a corresponding increase in temperature. It is obvious that a lamp Working under such conditions would be extremely wasteful of current and therefore commercially impracticable.

The object of the present invention is to provide for such a regulation of the current as will prevent any greater flow of current through the pencil than is necessary to maintain it at the desired point of incandescence.

The invention is hereinafter more fully described and claimed.

In the accompanying drawings, forming a part of this specification, Figure 1 is a sectional elevation of a lamp having myimprovement applied thereto. Fig. 2 is an enlarged detail view showing one form of my improved regulator, and Fig. 3 is a similar view illustrating another form of the same.

While the improvements are shown and hereinafter described in connection with the construction of lamp shown and described in application Serial No. 728,421, it may be used in connection with other forms of lamps, and the invention is not limited as regards the Serial No; 728,423. (No model.)

broad termsof the claims to any particular form or construction of pencil or body to be heated by the current.

Generally stated,the lamp is provided with a pencil 4, preferably formed of a material conductive only when heated, its conductivity increasing with increase in temperature. This pencil is supported on rods or pins 1 1, mounted in bearings 2 in the case or shell 3. These pins, which form the terminals of the wires 19, forming the exciting-circuit, have electrical contact with the terminals 7 of the pencil. The pencil maybe heated sufliciently topermit of the passage of the current by a lamp or candle; but it is preferred to effect the preliminary heating by the electric current flowing along a temporary conductor formed along the pencil from terminal to terminal. This temporary conductor is formed by causinga block 10, of graphite or other conducting material neutralizable at high temperatu res, to rub along the pencil from terminal to terminal. The graphite block is attached to a carrier-block 9 mounted on a threaded shaft 8. By the rotation of the shaft the carrier-block and graphite are moved alon g the pencil. As it is preferred to rotate the pencil while the block is moving over it, a driver-pinion 14 engages pinions on the shaft and the supporting-pin 1. For a more particular description and illustration of the lamp, which forms no part of the invention herein, reference should be had to application Serial No. 728,421, heretofore cited.

In order to prevent any increased flow of current beyond that necessary to maintain the pencil at the desired incandescence, a portion 24 of the circuit is formed of a material Whose conductivity will be suddenly and abnormally reduced by the passage of a greater current than that which such portion of the conductor is proportioned to carry- It is immaterial what change, molocular or otherwise, is produced in such portion, provided 5 that after the flow of current is reduced to or below normal such portion of the circuit will resume its original condition.

In the form illustrated in Figs. 1 and 2 the portion 24: of the circuit is formed by a piece of lead Wire of suitable size to permit, with out material molecular or other elemental change, the necessary passage or How of the amount of current for maintaining the desired incandescence of the pencil. As soon as the pencil is heated to the desired point, and thereby assumes a condition permitting of a greater flow of current, the Wire will become softened by such increased flow and present a greatly and suddenly increased resistance, so that less current will flow through the pencil, thereby permitting a cooling down of the pencil. Such cooling down of the pencil will further increase the resistance in the circuit, thus reducing the current flowing through the portion 24, thereby permitting it to resume practically its normal condition and the consequent restoration of practically the normal flow of current through the pencil and its restoration to normal incandescence. In order to prevent the rupture of the lead section when softened by'an increased flow of current, it is inclosed in a tube 25, formed of a material, such as glass, which will not serve as a conductor and capable of withstanding the temperature to which the lead is heated. In lieu of the lead any other material which will be so changed elementally or molecularly by a slightly abnormal How of current as to present an abnormally and suddenly increased resistance may be employed. Such a material is found in an alloy of nickel, iron, and copper. It is characteristic of this alloy that its resistance increases abnormally at a certain point when heated, so that if a portion, as 24*, of the circuit be formed by a wire of alloy it will operate to prevent any abnormal flow of current to the pencil. As under the conditions of use the current will be restored to practically normal conditions in the manner heretofore stated before the Wire 24 can be melted, no protecting or retaining tube need be employed. The portion 24 of the circuit is so proportioned that with a normal flow of current its resistance will not be abnormally affected-that is to say, the increase in resistance with normal flow will not be greater than that calculated by using the temperature coefficient of resistance as given in the text-books; but it will be so raised in temperature or otherwise affected by the normal current that a slight increased flow of current will produce a softening or such other molecular change that there will be a sudden increase in the tem perature coefficient of resistance due to such increased How.

I claim herein as my invention- 1. In an incandescent lamp, the combination of a pencil or body adapted to be highly heated by the passage of an electric current, and a resistance automatically increasable to an abnormal extent by a slight increase of current above the normal, connected in series with the pencil, substantially as set forth.

2. In an incandescent lamp, the combina tion of a pencil or body adapted to be highly heated by an electric current, and a circuit therefor, a portion of said circuit being formed by a conductor adapted to carry a normal current without material change and to present abnormally-increasing resistance on a slight increase of current above the normal in the circuit, substantially as set forth. I

3. In an incandescent lamp, the combination of a pencil or body adapted'to be highly heated by an electric current and a circuit therefor, a portion of said circuit being formed of lead adapted to carry the normal current without material change and to be so heated as to present an abnormally-increased resistance on a slight increase of current above normal, substantially as set forth.

In testimony whereof I have hereunto set my hand.

REGINALD A. FESSENDEN.

Witnesses:

DARWIN S. WOLCOTT, M. S. MURPHY. 

